Split lane traffic is the traffic that travels along a road segment that splits or is otherwise divided into two or more downstream road segments. Split lane traffic may sometimes create a bi-modality condition in which traffic in some of the lanes moves at a higher speed than traffic in other lanes. For example, a road segment may be upstream of two or more diverging downstream road segments, such as an exit ramp that exits to the right or left of an ongoing roadway. In some instances, the traffic in the lanes that are utilized to access the exit ramp may slow to a greater degree than the traffic in the other lanes that generally proceeds onward past the exit ramp. For example, at rush hour or at other times at which the roadway carries an appreciable volume of traffic, the lanes from which the exit ramp is accessed may slow to a much greater degree than the traffic in the other lanes that is generally preceding onward past the exit ramp. At other times, such as in instances in which the traffic volume is relatively light, all of the lanes of traffic for the road segment upstream of the diverging downstream road segments may precede at approximately the same speed with little, if any, diminution of speed in the lanes from which the exit ramp is accessed.
Routing algorithms, such as routing algorithms employed by navigation devices, generally do not take into account the speed differential between different lanes of traffic, particularly in instances in which the speed differential is transient. As such, the routing algorithms may not perform as well as is desired when confronted with a bi-modality condition. For example, in instances in which the speed of traffic flow various significantly between the various lanes of a road segment upstream of the diverging downstream road segments, the routing algorithm may operate on the assumption that the traffic will move uniformly at the higher speed experienced by the lanes of traffic that proceed onward past the exit ramp without any appreciable diminution of the speed due to traffic delays in advance of the exit ramp. Consequently, a user or an autonomous vehicle that is relying upon the routing algorithm and who drives in the lane of traffic that is delayed in advance of the exit ramp may find that the estimated time of arrival provided by the routing algorithm may be incorrect. Depending upon the extent of the delay, the user also may be disappointed that the routing algorithm did not either direct the user to a different roadway or otherwise endeavor to avoid the lanes of traffic that slowed in advance of the exit ramp.